U.S. Pat. No. 4,091,056 discloses an arrangement for vaporizing liquids wherein a carrier gas flow is alternately conducted via a vaporizer or via a bypass line past the vaporizer to the consumer. The flow through the bypass line is conducted through a flow meter having an indicator which can be calibrated to the value zero for the flow then present. The carrier gas entrains a component of the vaporized liquid only when the carrier gas line is switched into the vaporizer whereby the mass flow increases and its increased component is indicated by the flow meter.
The precision of the indicated metered amount on the flow meter is dependent essentially upon how precisely the carrier gas flow is adjusted. The requirements as to the precision of the metering of the carrier gas are better fulfilled at high volume and mass flows than at very low mass flows such as a few milliliters per minute. These low mass flows are then significant when it is intended to supply anesthetic into a closed anesthetic loop from an anesthetic vaporizer. In this way, only such amounts of anesthetic are introduced into the carrier gas which are consumed or removed by possible small leaks from the breathing loop.